70s Ampeg V4B Blows Fuses

[g1]

How about DC volts at D6 anode or negative end of C15.
What is the make and model of your multi-meter?

[ca7922303]

C16 after replacement reads 150vac & 1.4 vac @ 60v on variac.

[ca7922303]

Replaced c15, c16, c23, r28. At 60v on variac, amp out of standby, c16(150.8v & 212mv), c15(-0.00mv +, -267mv -) c23(-0.00mv +), (-267mv -), r28(39mv & 16.63v and increases the constant hum when touched) power and preamp tubes are slightly lit, preamp tubes are cool, power tubes(2) are hot.also, no preamp control except for mid-range. Control knob and rocker arm have full affect on hum tone. All other control knobs and rocker switches do not.

[vintagekiki]

https://www.doktorsewage.com/operating-theatre-ampeg-v4b/

https://www.doktorsewage.com/operating-theatre-ampeg-v-4b-part-2/

[g1]

I have no crystal ball, but I do have a V4 (non-B) chassis open here.

[vintagekiki]

Some wires connect to trace side of circuit board.

[g1]

there should be a wired communication between the caps and the PCB (maybe I don't see it)

Some wires connect to trace side of circuit board.

[vintagekiki]

I think these are sometimes mounted elsewhere, off the board. Maybe on the filter cap cans.

I also saw this mode of mounting, but in that case there should be a wired communication between the caps and the PCB (maybe I don't see it)

[g1]

Missing R52, R53 (look in schematic for value).

I think these are sometimes mounted elsewhere, off the board. Maybe on the filter cap cans.

[vintagekiki]

Underside of board #210803-1 less c15, c16, c23. R28 is burnt and OL on all ranges, will replace. Anything in photos look wrong?

Missing C16 (look in schematic for value). Therefore no bias voltage.
Missing R52, R53 (look in schematic for value). Slowly compare PCB layout with the schematic, see what is different, eliminate what is wrong, and then ask questions.
When you remove all what is wrong, remove the power tubes, measure whether all DC voltages on the rectifier are within limits, and then mount the power tubes.

https://www.ampegv4.com/images/schematics/V4B.jpg

[vintagekiki]

Rest of board

Replace damaged R28 look in schematic for value

[ca7922303]

Rest of board

[ca7922303]

Underside of board #210803-1 less c15, c16, c23. R28 is burnt and OL on all ranges, will replace. Anything in photos look wrong?

[g1]

I should have not posted the title Blows Fuses. I have not had it blow a fuse yet. Guy I got it from told me it blows fuses and in my hurry to get advice on this amp, I prematurely posted it that way. But no, it does not blow fuses, tubes in or out.

If you do not have the proper DC bias at pin5 of the power tubes, you should not run it with them installed. If it does not blow the fuse it will red-plate the power tubes and damage them.
So double check that. Without the power tubes installed, you should have around minus 60VDC at pin 5 of all power tubes. Maybe it is there and you just need to dig in more with the meter probes.or maybe you weren't on pin5 when you checked before.

[ca7922303]

I've got board#210803-1 and it seems identical to the schematic I'm looking at on the ampeg website dated 12/71.